Friday, October 15, 2010

When monarchs get sick with a parasite that might hurt their offspring they go to the drugstore

Scientific American notes researchers are discovering humans aren't the only creatures which seek out plants for their medicinal qualities. There's a growing body of evidence showing that animals also do so.

The most recent example involves the monarch butterfly. Monarchs feed on milkweed and lay their eggs on the plants because milkweed contains a chemical that makes monarchs toxic to their predators. There are many species of milkweed, and they vary in their concentration of the chemical, which in higher concentrations has medicinal qualities for caterpillars infected by their mothers with a parasite that would otherwise be fatal. And monarchs seem to selectively seek out these milkweeds as egg-laying sites when they are infected.

Some milkweeds have a higher concentration of chemicals called cardenolides, which make the butterflies toxic to predators. Research had focused on whether the monarch’s chose different milkweeds to hurt their enemies.

But Emory University’s Jaap de Roode wondered if the choice might be related to a parasite that’s passed from mother to offspring, with fatal results: “What we do find is that the monarchs prefer to lay their eggs on the medicinal species when they are infected. However, when they are not infected with the parasite, they do not prefer this species over this one, they lay their eggs equally between these two species. So somehow they know that they’re infected and they know what to do about it.” The research was published in the journal Ecology Letters. [Thierry Lefèvre et al., "Evidence for trans-generational medication in nature"]

Amazing. And you can't help wondering how that works in practice. Does a monarch wake up feeling sick and fly off to the nearest milkweed pharmacy, like a human picking up some flu medication on the way home? Or is it a more unconscious process?